The present invention relates to gas turbine engines and more particularly to a unique method and apparatus for increasing the efficiency of a turbine engine compressor by introducing temperature stratified air into its inlet.
For improved efficiency of a gas turbine cycle engine, it is desirable to design a turbine compressor with high pressure ratios and with a minimum of compressor stages for reduced weight and cost. In small gas turbines, a single high pressure ratio centrifugal compressor stage is often utilized.
As the pressure ratio of the compressor stage is increased, it is necessary to increase the rotor blade tip velocities and relative gas velocities. As the relative gas velocities exceed the speed of sound (Mach 1.0), however, shocks develop in the compressor and flow losses occur. The flow first becomes supersonic at the blade tips of the first compressor stage in axial compressors, or at the inducer blade tips of a centrifugal compressor stage. When the relative Mach number of the inlet blade tip becomes excessive, strong shock patterns develop and compressor efficiency and flow capacity decrease. This occurs even though the relative Mach numbers at the mid and inner (hub) portions of the rotor blades remain at subsonic velocities.
The present invention has its overall object to improve gas turbine engines and more particularly to improve the efficiency of the compressors of such engines. Another object is to improve the efficiency of a single-stage high pressure ratio turbine compressor for use with a Brayton cycle engine or with an integrated combinbed Brayton-Rankine cycle engine (IBRE). A further object is to reduce the relative Mach number of the inlet fluid to a gas turbine engine compressor in the area of the rotor blade tips in order to prevent or reduce supersonic shocks in the engine. A still further object is to temperature stratify the inlet fluid to the compressor to increase the efficiency thereof.
These and other objects are achieved by the present invention where the inlet fluid entering the compressor is temperature stratified into two portions and the higher temperature fluid is injected in the area of the rotor blade tips. The higher temperature portion of the stratified inlet fluid may be derived by recirculating part of the engine exhaust which is at a higher temperature than the ambient air. The higher temperature fluid at the blade tips reduces the relative Mach number.
Still further objects, features and advantages of the invention will become apparent upon consideration of the present disclosure and the accompanying drawings and claims.